1. Field of the Invention
The present invention relates to a flux-cored wire, and particularly to a flux-cored wire for low alloy steels and high alloy steels which is excellent in arc stability and in moisture absorption resistance of fume and slag.
2. Description of the Related Art
In the conventional flux-cored wire, as shown in Conventional Examples in the preferred embodiments described later, a flux containing various components is filled in a metal sheath, and an Na compound is mixed in the flux in an amount of about 1.5 to 6 wt % (Na.sub.2 O equivalent amount) for improving arc stability.
In bead-on-plate welding, horizontal fillet welding, or multi-layer welding using a flux-cored wire, there is a fear that fume generated during welding adheres on the bead surface and the base material surface in the vicinity thereof, or slag remains at the bead toe portion and the bead surface. As for the residue of slag, since a flux-cored wire for low alloy steels or high alloy steels contains a large amount of alloy components in flux, it is inferior in the slag releasability to a flux-cored wire for mild steels, so that the slag tends to remain on the bead without being released. The reason for this is that oxides of alloy components in flux (in particular, oxides of Nb, Cr, and Ti) are concentrated between the slag and the welding metal surface, which functions as a binder. Accordingly, the flux-cored wire has such an essential property that the slag is liable to remain on the bead surface.
The fume generated on the bead surface or the base material surface in the vicinity thereof during welding operation, and the slag remaining on the bead surface tend to absorb moisture. Consequently, when multi-layer welding is performed on the bead and in the vicinity thereof in such a state, there arises such a problem that pits and blow-holes are generated on the next pass bead. In particular, in the welding operation under a high temperature and high moisture condition, the above problem significantly appears.